Sheet alignment modules for post-processing devices are known as sheet stack joggers. Commonly applied in oppositely placed pairs of joggers.
Commonly two elements are positioned at opposite sides of a stack of sheets and are actuated to knock at least the top of the stack to be able to align the last fed sheet to be aligned with the rest of the stack.
However, in order to produce staggered stacks, i.e. stacks which have subsets of sheets in stacks which have another orientation than the main stack, e.g. to identify separate jobs in a larger print operation, knocking the top portion of the stack may disorient the separate sub-stacks in a staggered collection. To be able to knock only the single top sheet without disturbing the rest of the stack may be cumbersome or requires a very precise mechanism of knockers.